The present invention relates to positive, i.e., radiation-solubilized, radiation-sensitive mixtures suitable for the production of photoresists, electronic components and printing plates and for chemical milling. More particularly, it relates to radiation-sensitive mixtures which contain,
(a) a compound which forms a strong acid on irradiation, PA1 (b) a compound containing at least one acid-cleavable C-O-C bond and PA1 (c) a binder which is insoluble in water and soluble in aqueous-alkaline solutions, PA1 (a) a compound which produces a strong acid under the action of actinic radiation, PA1 (b) an acetal, and PA1 (c) a binder that is insoluble in water and soluble in organic solvents and aqueous-alkaline solutions,
Mixtures of the compositions mentioned are described, for example, in U.S. Pat. Nos. 3,779,778; 4,101,323; and 4,189,323; in German Offenlegungsschriften Nos. 2,718,254; 2,928,636; and 3,151,078, and in European Patent Application Nos. 0,006,626; 0,006,627; 0,022,571 and 0,042,562.
On exposure of these materials, photolysis of compound (a) forms an acid which causes cleavage of C--O--C bonds of compound (b), meaning that
the exposed areas of the photosensitive coatings become soluble in the developer. However, these mixtures are not free of disadvantages.
The polyacetals and polyorthoesters preferred hitherto are in some cases not readily accessible and/or have the property--depending on the condensation conditions--of being produced in various molecular weight distributions. This influences both the production costs and the copying properties desired, in particular the constancy of photosensitivity of photosensitive coatings produced therefrom. These known photosensitive mixtures can only contain a certain amount of acid-cleavable compounds; the major component they contain is generally a binder that is insoluble in water but soluble in aqueous alkalis, which gives the mixture adequate overdevelopment resistance However, this large proportion of alkali-soluble binder, preferably phenolic resin, has the effect that, in particular at relatively great coating thicknesses, coatings of the mixture are relatively brittle and tend to crack or splinter.
The opinion prevailing hitherto was that, for good image differentiation, the greatest possible number of cleavable C--O--C bonds must be present, i.e. polymeric compounds, whereby the C--O--C bonds are preferably in the main chain of the polymer, so that many small, essentially more soluble fragments are formed from one polymer molecule.